Charts, SQL Views, SQL Alerts, and SQL Snippets store their previous SQL and settings, making it easy to revert back to a previous state. Clicking into the history tab on the right side of the editor shows a log of what changes were made, who made them, and the time that the change was made.
To revert to a previous state, hover over the desired version and click apply. This automatically triggers the applied version of the query to re-run. Once the previous version has been restored, the chart will need to be saved in order for the change to be reflected on the dashboard.
If a user is deleted from a site, their name will not appear in the version history, but their previous changes will still be accessible.